This invention relates generally to aquaria and particularly to a cost effective apparatus for generating a time-varying surge in a saltwater reef aquarium.
Reef aquaria contain organisms that evolved in a tidal environment where tidal processes presented an ever-changing flow of nutrients and removal of waste products. In the restricted aquarium environment a lack of appropriately varying circulation can cause waste product buildup (especially in living coral) and reduce the amount of nutrients available to other organisms such as anemones. Waste buildup can cause coral death and susceptibility of other animals in the tank to disease.
Thus methods and apparatuses for causing a dynamically changing circulatory pattern in the salt-water reef aquarium is of practical importance and essential to the well being of the animals in the tank.
To sense the difficulty of the problem one has only to view a toy snow globe with a battery-operated circulator. These globes generally appear on the market every year around Christmas. If one turns on the circulator and initially shakes the globe to insure uniform initial “snow” particle distribution, it only takes a short time for all the “snow” particles to be deposited on the scenic elements of the globe in stationary fashion. The globe has reached steady state with respect to the snow particles even though the circulator continues to move the water within the globe. Think of these “snow” particles as food and/or waste particles in a reef tank.
The general problem of causing a changing flow environment in a reef tank so as to roughly simulate a tidal ocean environment is referred to herein as generating a “reef surge”.
There are a number of methods that have been used in the past to generate a reef surge in an aquarium. The majority of these employ mechanical devices that couple with the output fitting of a pump and vary the direction of flow over time in a cyclic manner. Aquaria using these devices quickly reach steady state.
One particularly clever, if decoratively and operationally challenging prior-art solution, is an adaptation of the British elevated water closet: water is pumped up to a reservoir above the aquarium and dumped at regular intervals back into the aquarium. Such an approach causes a cyclic momentary pounding turbulence in the tank that can dislodge tank animals and damage coral.
Electronic prior-art solutions revolve around solid-state relays for turning one or more submersible pumps on and off at pre-determined intervals. These approaches represent a step in the right direction but have limited effectiveness, as they yield no output flow variability.
An electronic solution wherein the flow rate of a submersible pump is varied over time would offer an immediate improvement over the above approaches.
Submersible pumps used in aquariums are almost exclusively AC permanent magnet synchronous motor (PMSM) pumps. These pumps are available with maximum flow rates from approximately 25 gallons-per-hour (gph) to approximately 10,000 gph. Low voltage (i.e. 12VAC) implementations of these pumps, because of market demand, are currently only available for maximum flow rates under 200 gph. In the United States the majority of PMSM submersible pumps run on 110 VAC. Regardless of their design voltage, the speed of such pumps (which is related to the no-load zero-head flow rate) can only be varied by methods that vary the frequency of the waveform supplied to the pump.
U.S. Pat. No. 6,717,383 (co-invented by the present inventor) teaches a cost effective variable frequency drive for controlling PMSM submersible pumps of the type in widespread use in small fountain applications. The generated AC waveform is essentially a variable-width square wave pulse separated by a variable width-dead time. Pending utility application entitled “Variable Frequency, Drive for AC Synchronous Motors with Application to Pumps” by the present inventor provides novel, cost effective embodiments which reduce pump vibration in larger AC PMSM pumps; these have decided utility in the larger tank home aquarium arena.
Application of either of these above referenced electronic technologies in the previous paragraph to the problem of generating a reef surge would constitute a considerable improvement over the prior art. For instance, a single pump could be made to follow a complex sequence of flows with varying inter-flow ramping. Randomness could be introduced in both the sequence of flow rates and the time intervals between successive flow rates. Or, the variation of flow could be made to simulate a time-of-day dependent real-world tidal pattern. Further by adding multiple synchronously or asynchronously controlled pumps strategically located within the tank, a distributed surge could be realized. To the inventor's knowledge no such reef control surge variation protocols have been reported not alone implemented. One aim of this invention is to implement such control schemes in a reef surge apparatus that provides improved dynamically changing circulation in a reef aquarium.
A further considerable improvement would involve generating a dynamically changing forward and reverse flow of water from a single pump dedicated to creating reef surge in a salt-water reef tank. This is another aim of this invention.